Subcaliber projectile and sabot for high velocity firearms



Sept. 15, 1964 E N HEGGE ETAL 3,148,472

SUBCALIBER PROJECTILE AND SABOT FOR HIGH VELOCITY FIREARMS Filed June ll, 1962 BY John P. Mnl] mnu-gh 'ein para

3,43,472 SUBCALBER PR'GJECTLE AND SABOT FR HEGH VELCEETY Fili-@ARMS Edward N. Hegge, Walpole, and Eohn P. MfcDonough,

Concord, Mass., assignors to the United States of America as represented by the Secretary oi' the Army Filed lune 11, 1962, Ser. No. 20,'739 7 Ciaims. (Ci. i2--1) (Granted under Title 35, US. Code (1952), sec. 266) l0 rl`he invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to sabots for subcaliber projectiles and is more particularly directed to an improved plastic carrier which is adapted to be positively retained on the projectile while in the bore of the gun barrel and yet may be readily and completely discarded upon emergence therefrom without any adverse effect on the flight path imparted to the projectile.

It is well known that the target capability of modern weapon systems can be substantially improved by increasing the muzzle velocity at which the projectile is launched therefrom. One method by which such improvement may be accomplished lies in reducing the calibe of the projectile and providing a carrier or sabot of suiicient diameter to maintain the necessary gas sealing contact with the bore surface of the barrel. Since the increase in the muzzle velocity of the subcaliber projectile is directly proportional to the weight of the sabot, current design of high velocity ammunition is directed to the utilization of sabots fabricated from lightweight plastic materials.

While these plastic sabots enable the transfer of maximum energy to the projectile and, consequently, permit muzzle velocities in excess of 1000 ft. per second, considerable difliculty has been experienced in preventing relative movement between the sabot and the projectile prior to emergence from the barrel of the gun. This undesirable slippage of the sabot will, of course, reduce the maximum velocity which can be imparted to Ithe projectile and is partly due to the fact that the lightweight plastic material of the sabot provides less resistance to starting movement than the heavier mass of the projectile. Furthermore, once the frictional grip between sabot and projectile has been broken or substantially reduced by the accelerative forces thereon, subsequent relative movement therebetween is promoted by the fact that the frictional area of contact between the sabot and the bore of the barrel is greater than the corresponding contact area between the sabot and the exterior surface of the projectile.

Such drawback in the utilization of plastic sabots has been recognized in U.S. Patent No. 2,939,395 which teaches the concept of increasing the frictional engagement between the plastic sabot and the metallic projectile by the provision of a rearwardly extending conical pressure surface on the sabot designed to promote the constriction thereof against the projectile in response to the pressures exerted by the propellant gases. However, subsequent experimentation has indicated lthat a conical pressure surface of this type offers little or no improvement in the ballistic action of the projectile over comparable sabots with nontapered exteriors. Accordingly, it is necessary =to look elsewhere in an effort to overcome the detrimental effects of the variations encountered in the starting coefhcient of friction between a plastic sabot and a metallic projectile as a result of such changeable factors as atmospheric dust and humidity, oxide films, surface finish, vibration, contaminants such as grease and oil, and variations in dimensional tolerances.

ii- Patented Sept. l5., 19%4 Since the prevention of slippage between a plastic sabot and `the projectile engaged thereby cannot be satisfactorily accomplished merely by the application of force to the exterior of the sabot, it has been suggested that a force or press lit be utilized in the assembly thereof. While the interference created by such tit would improve the frictional engagement between the sabot and the projectile, the adoption of this technique on a mass production basis has not been considered in view of the relatively costly machining required. It has also been suggested that the required improvement in the frictional engagement between the sabot and the projectile could be obtained by shrinking the sabot onto the projectile by means of judicious heating and cooling procedures. However, the excessive amount of shrinkage required to obtain the desired frictional engagement introduces several undesirable collateral eifects. For one thing, the heating and cooling of the plastic material promotes excessive brittleness therein which could lead to actual cracking during the handling required to assemble the various components into a complete round of ammunition. In addition, many plastic materials are subject to creep over a period of time and, therefore, the original shrinkage tit would deteriorate during the necessary storage of the ammunition.

Accordingly, it is an important object of this invention to improve the engagement between a plastic sabot and a metallic projectile without the necessity for increasing the normal pressures produced in the contact between metal and heat resistant plastic of high impact strength.

It is a more specific object of this invention to provide an improved plastic sabot for a metallic projectile wherein a portion of the mating surfaces therebetween are deliberately contoured to form a shear area capable of resisting relative movement between the sabot and the projectile during the passage thereof through the bore of the gun barrel.

A further object of rthe present invention resides in the provision of an improved sabot and projectile assembly wherein the configuration of the contacting surfaces therebetween is particularly selected to increase the setback forces imparted to the projectile during acceleration through the gun barrel and thereby augment the normal frictional forces therebetween for -the purpose of preventing relative movement of the parts While Still within the bore of the gun barrel.

It is readily apparent, however, that any increase in the engagement between a sabot and a projectile introduces a corresponding difficulty in the ease with which the sabot can be discarded immediately upon emergence from the muzzle of the gun barrel. Prior art expedients of fabricating the sabot in separate parts or in the provision of prior slits or grooves designed to weaken the material does not insure the complete and uniform disintegration thereof. Thus, in ythe event the sabot is discarded in fragments of substantial size, it is entirely possible for the rear end of the projectile, especially if larger than the front end thereof, to strike such fragments upon emergence from the bore of the gun barrel and, consequently, incur substantial deviation from the true path of flight imparted thereto by the gun barrel.

The ineffectiveness of the sabot stripping arrangements of -the prior art is recognized in U.S. Patent No. 2,811,901 which teaches the utilization of a separate attachment to the muzzle end of the gun barrel for separating the sabot from the projectile. While such device ensures more positive and reliable results over those previous attempts which depended upon pre-existing weakness in the sabot material, it still does not provide the effective discarding of the sabot required in military designs. One problem to be solved is the frequent replacement necessitated by the abnormal wear of the cutting ridges formed therein. Another is the undesirable effect produced in a the true ight path of the projectile by the shock encountered in the abrupt contact between the sabot and the reduced diameter of the stripper at the critical movement at which the muzzle end of the barrel is establishing the flight path of the projectile.

Accordingly, it is a further object of this invention to provide an improved sabot and projectile combination which will cooperate with a change in the internal configuration of a gun barrel to prepare the sabot for immediate disintegration upon emergence from the gun barrel.

A specific object of this invention is to provide the interior bore of a gun barrel with integral means for stressing or otherwise weakening a plastic sabot during the period in which the pressure of the propellant gases has begun to fall from the peak point thereof to thereby ensure complete disintegration of the sabot immediately upon emergence from the gun barrel.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

FIG. l is a cross-sectional representation of a plastic sabot which is retained on a fin-stabilizing subcaliber projectile by a shear-type interference;

FlG. 2 is a view similar to FIG. l but showing a structure wherein the shear-type interference is provided by a plurality of spaced conically tapered sections in the projectile. In addition, the opening in the forward end of the sabot is enlarged in order to expedite the disintegration thereof upon emergence from a gun barrel, such opening being filled with a relatively weak plastic material in comparison to that utilized in the sabot;

FG. 3 is a view similar to FIGS. l and 2 but showing a projectile and sabot combination wherein the shear-.type interference is provided by the mating engagement between a pair of divergently tapered conical sections in the projectile and a corresponding pair of oppositely tapered sections in the sabot;

FIG. 4 is a longitudinal sectional view showing a sabot assembled to a fin-stabilized projectile having an annular section of reduced diameter, the combination being shown during the passage thereof through a gun barrel having a plurality of enlarged diameter regions therein which are consecutively spaced to impart pulsating movement to the sabot for preconditioning the plastic material therein to disintegrate immediately upon emergence from the muzzle end of the gun barrel;

FG. 5 is a longitudinal section of the muzzle end of a gun barrel wherein the bore terminates in an enlarged diameter region having a plurality of knife-edged wedges circumferentially spaced about the forward end thereof to weaken the plastic material of the sabot subsequent to the expansion thereof into the enlarged diameter region. In lthis view, the projectile includes an annular shoulder formed by an inwardly tapered conical section; and

FIG. 6 is an end view of the structure shown in FiG. 5.

inasmuch as extensive experimentation with weapons of military design has clearly demonstrated the desirability of increasing the velocities at which the projectiles can be fired therefrom, efforts are under way to reduce the size and mass of the projectiles without the introduction of a corresponding decrease in accuracy or terminal ballistic effects. One of the more successful approaches in this direction has been a change in the configuration of the projectile from the conventional blunt ended cylinder to a needlelike structure having a plurality of ns at the rear end thereof for stabilization in flight. Accordingly, the sabot of the present invention is hereinafter described in conjunction with this type of projectile which, when of light weight and size, is commonly referred to in the art as a flchette However, it shouldjbe understood that the principles of the sabot-projectile combination of the present invention may also be applied with equal success to larger projectiles of arrow type as well as those of conventional shape.

Vincrease the gas sealing effect in this critical area.

In FIG. l there is disclosed a projectile l@ having an elongated cylindrical body 12 whose length is at least three to four times greater than the cross-sectional diameter thereof. A plurality of relatively thin blades or fins 14 are disposed at the rear end of body 12 for stabilization thereof during flight toward the target. Body l2 is annularly enlarged at a point located in the forward third thereof to form an annular shoulder i6. The remainder of body i2 continues forwardly therefrom in a conical taper to form an arrowhead configuration 18 terminating in a sharp point. Projectiles of this type may range from an extremely small weight of ten grains to one as heavy as eight ounces.

Projectile l@ is arranged to be carried through the bore of a gun barrel by a sabot Ztl fabricated from any heat resistant plastic material of high impact strength capable of absorbing a relatively high strain rate in response to the pressures encountered during passage thereof through the bore of a gun barrel. Experience has shown that excellent results are provided by thermosetting plastics such as a phenolic resin filled with fibers of cotton flock, Daeron, or asbestos.

Sabot 20 may be press or shrink fitted onto projectile 10 prior to the installation or formation of fins 14 thereon. In order to utilize these assembly techniques, sabot 20 is axially bored, as shown at 22, to provide an interior configuration designed to mate with arrowhead 18. This may be accomplished by ultrasonic cavitation or other similar techniques of forming openings of irregular contour. If the frictional engagement of the press fit is insufficient, sabot 20 may be heated prior to assembly onto projectile l0. Since the coefficient of thermal expansion of plastic is much greater than that of metal, the required interference fit will be achieved upon cooling. However, it has been found that the simplest and least expensive method of assembling the sabot to the projectile with the proper frictional engagement therebetween lies in the technique 0f molding the sabot under pressure onto a projectile whose surface has been thoroughly cleaned and dried.

Regardless of the particular method employed in the fabrication of sabot 20, the exterior diameter thereof is selected to be slightly larger than fins 14 and, at the same time, to provide a snug, gas-sealing fit in the bore of the gun barrel. In fact, the rear end of sabot 20 may be suitably dished or recessed, as best shown at 24, to The forward end of sabot 2f) is exteriorly tapered, as shown at 26, to progressively reduce the cross-sectional thickness thereof in order to facilitate the initiation of sabot disintegration while still in the bore of the gun barrel. This is accomplished by the pressure build-up of the air trapped in the space between the walls of sabot bore 22 and the exterior surface of the tapered front end of projectile l0. In fact, the forward end of sabot 20 may be provided with an enlarged entry 28 to accelerate the accumulation of air into sabot bore 22.

If desired, the initial break-up of the sabot, while still Within the gun barrel, may be even further accelerated by reducing the cross-sectional wall thickness at the forward end thereof. This may be accomplished by gradually increasing the diameter of sabot bore Z2 from a point adjacent the beginning of arrowhead configuration 18 as best shown at 30 in FIG. 2. However, in order to prevent accidental breakage as well as the accumulation of dirt or other foreign matter during handling of the ammunition, enlarged opening 30 is preferably filled with a relatively weak plastic material 331 designed to fracture under the increasing air pressure against the front end thereof during passage through the rearm barrel.

Once the complete unit shown in FIG. l is tired, sabot 20 tends to respond more quickly than the heavier mass of projectile 10 to the forces created by the rapid expansion of the propellant gases. Ordinarily, this condition would lower the frictional engagement between sabot 20 and projectile 10 to such an extent that slippage theresali-sara between could readily occur. However, with the structure illustrated in FIG. l, any tendency for sabot 2i) to move forwardly relative to projectile is positively blocked by annular shoulder 16 thereon. While the projection of shoulder 16 from body 12 of projectile 10 detracts from the desired smooth aerodynamic surface thereof, the resulting loss in velocity and accuracy is far outweighed by the beneficial effects achieved through the absence of any slippage between sabot 20 and projectile 1t) during the travel thereof in the gun barrel. lf desired, annular shoulder 16 may be formed by an inwardly tapered conical section 29 as best shown in FIG. 5.

In the event a single shear interference fit does not succeed in preventing movement of the sabot relative to the projectile, the latter may be formed with a series of successive conical tapers 32 disposed along the exterior surface thereof in sawtooth formation as best shown in FIG. 2. In this construction, the setback and other forces tending to promote relative movement between the sabot and projectile are linearly distributed therealong instead of being concentrated in one area.

However, in some instances the retention of a smooth aerodynamic surface does assume significant importance. In such event, the required shear interference may be accomplished by the configuration shown in FIG. 3 wherein a flechette projectile 34 is provided with a reduced diameter section 36 formed by tapered forward and rearward portions 38 and 40 which converge to meet at the smaller diameter ends thereof. The sabot 42 selected to carry such projectile 34 is similar to sabot 20 except that the interior bore is constricted, as shown at 44, to provide intimate contact along the entire exterior surface of the reduced diameter section 36 of projectile 34.

Once projectile 34 is fired, the disparity in the relative areas on which the propellant gases act and the difference in the relative weights of the sabot and projectile create setback forces which increase the normal pressure component therebetween. Thus, the customary tendency for sabot 4Z to move forwardly relative to projectile 34 is resisted not only by the shear interference contact between the mating surfaces of sections 36 and 44 but by the increase in the normal pressures produced by the setback forces on projectile 34. In View of the converging arrangement of conically tapered portions 38 and 40, the resulting resistance to movement of sabot 42 relative to projectile 34 is achieved in both axial directions.

lf preferred, the reduced diameter section in the projectile may be formed by concave indentations 45 in opposite sides thereof as best shown in FIG. 4. The interior bore of the sabot is, of course, shaped to provide intimate contact throughout the length of the reduced diameter section.

Since the sabots described above are preferably constructed of a thermosetting plastic material, such as a phenolic or similar resin illed with cotton flock or asbestos fibers, the exterior configuration thereof rapidly conforms to the shape of the gun barrel bore in response to the extremely high forces and heat involved in the attainment of the peak gas pressure. Under ordinary circumstances, this change in the shape of the sabot continues until the emergence thereof from the bore of the barrel whereupon disintegration thereof will begin to take place in accordance with the stresses and strains introduced in the plastic material by the heat and pressure imparted thereto during the expansion of the propellant gases. While the normal disintegration of the plastic material from which the sabot is composed is entirely adequate where the projectile is being pushed thereby through the bore of the barrel, such is not the case where the sabot is located at the forward end of the projectile to impart a pulling action thereon down the barrel bore. ln this manner of propulsion, the finned end of the projectile passes through the area occupied by the disintegrating fragments of the sabot and it is, therefore, essential that the size of these fragments be kept to a minimum.

It has been found that the break-up of the plastic material is dependent upon the stresses and strains introduced therein during the passage thereof through the barrel bore. Subsequent experimentation has clearly indicated that these stresses and strains may be significantly multiplied by crushing the plastic material during the period in which the peak pressure of the propellant gases is decreasing. Additional experimentation in this respect has clearly demonstrated that this may be accomplished by a decrease in bore diameter at or near the muzzle end of the barrel. This dimensional change may be obtained either by a forwardly tapered portion or by a corresponding gradual increase in the corrosion-resisting plating normally applied to the interior surfaces of barrel bores.

However, it has been discovered that the preconditioning of plastic sabots of the foregoing types for complete disintegration immediately upon emergence from the bore of the barrel is best achieved by a series of expanded diameter regions 46. As shown in PEG. 4, the normal diameter of a barrel bore it is gradually increased as indicated by the inclined portion at 56 to a maximum which is continued for a distance between one and two times the length of sabot Zti. Thereafter, the diameter of barrel bore 43 is gradually decreased as shown at 52 to the original size thereof. Although the inclined end portions Sti and 52 of each expanded diameter region 46 are shown as equal in length and slope, it may be desirable to provide a steeper and shorter incline at one end than the other. The central linear portions of regions 46 may all be of the same diameter throughout or may progressiveiy increase in diameter as the distance thereof from the muzzle end of barrel bore 48 is decreased. While the quantity and spacing of regions 46 will Vary in accordance with the degree of stress and strain required in the plastic material `in order to obtain the desired rapidity of disintegration, the first region must be located in barrel bore 48 forwardly of the point at which the pressure of the propellant gases reach a peak. Under normal conditions, this will occur beyond the first third of barrel length. It should also be understood that, although the increase in the diameter of region 46 over the normal diameter of barrel bore 48 is exaggerated in the drawings, nevertheless, the actual dimensional change is significant and provides substantial transverse movement of the plastic material in the sabot.

However, regardless of the configuration and location of these expanded diameter regions 46, the extremely rapid expansion and compression of the Sabot will produce infinitesimal cracking throughout. Since the plastic material of the sabot becomes relatively brittle in response to the high heat and pressure incurred during the initial stages of acceleration in the barrel, the disturbance of the arrangement and location of the fibers dispersed throughout the plastic will produce the type of cracking which will result in the complete disintegration of the sabot upon emergence from the rigid confines of barrel bore 4S.

In the event the disintegration of sabot 20 requires still further improvement, this may be accomplished by incorporating suitable projections within the interior of barrel bore 48 which will slit or score the plastic material so -as to weaken the resistance thereof to distintegration upon emergence from the muzzle end of the barrel. it has been found that the necessary weakening may be produced by a plurality of parallel knife-edged wedges 54 circumferentially spaced about the interior surface of barrel ybore 4d adjacent the muzzle end thereof as shown in FIG. 5. In this design, the normal diameter of barrel bore 48 is enlarged by a relatively short and steep incline 56 and this enlarged diameter region 5d is continued out to the muzzle end of barrel bore 43.

Wedges 54 are formed with beveled sides which originate at a common point and extend forwardly in a divergent manner to provide a triangular configuration preferably, although not necessarily, terminating at the muzzle end of barrel bore 48. At the same time, the radial projection of each wedge 54 from ithe surface of barrel bore 48 is progressively increased to reach a maximum at the point of forward termination. The beveled sides of wedges 54 form a continuous cutting edge 62 designed to slice through the expanded plastic material passing through enlarged diameter region S8 and form slots of increasing depth and width. Such scoring or cutting of the sabot weakens the plastic material therein immediately prior to the emergence thereof from the muzzle end of barrel bore 48. At the same time, the progressively increasing height of wedges 54 gradually compresses the corresponding portions of the sabot back to the normal diameter which existed prior to the passage thereof through the enlarged diameter region 58 of barrel bore 43. Such compression actually crushes the plastic material and introduces the infinitesimal cracking therein which preconditions the sabot for immediate disintegration upon emergence from barrel bore 48. Since the compression of the plastic material is limited to the action of wedges 54, it is important that the total area of contact thereof with the exterior periphery of the sabot exceed the total of the noncontacting areas between Wedges 54.

Thus, there is here provided a simple and inexpensive sabot which is particularly useful with arrowhead type of projectiles and can be retained thereon in a variety of ways dependent upon the degree of frictional force required tto positively resist relative movement therebetween during the travel thereof through the bore of a gun banrel. Where a minimum amount of friction is required, this may be readily accomplished by molding the sabot under pressure onto a thoroughly dry and clean surface of the projectile. If a greater amount of resistance to setback and accelerative forces is required, this may be accomplished by introducing the previously described shear interference tits between the sabot and projectile.

If maximum engagement therebetween is necessary, the

shear interference lits may be -augmented by shrinking the plastic sabot onto the projectile.

Furthermore, the present invention includes means for preconditioning the sabot in order to effect the discard thereof from the projectile immediately upon emergence from the bore of :the barrel despite the improved engagement provided between the sabot and projectile. This preconditioning may be accomplished by subjecting the sabot to a series of extremely short pulsations designed to provide infinitesimal cracking in the plastic material prior to the emeregence thereof from the bore of the gun barrel. If an additional degree of preconditioning should be required, this may be accomplished by a plurality of projections judiciously located in the bore of the barrel and arranged to score or slit the plastic material of the sabot. Since the deformation of the sabot is accomplished entirely within the bore of the barrel, the projectile is acceurately launched without the undesirable shock normally encountered in the passage of the sabot through a separate stripping device attached to the muzzle end of the gun barrel.

Although a particular embodiment of the invention has been described in detail herein, it is evident that many variations may be devised within the spirit and scope thereof and the following claims are intended to include such variations.

We claim:

l. A projectile and sabot configuration comprising an elongated subcaliber projectile having a plurality of radially disposed stabilizing 'tins at one end thereof and a conically tapered portion at the other end thereof terminating in a point, means forming an annular change in diameter around the exterior periphery of said projectile adjacent said conically tapered portion, and a sabot of thermosetting plastic material comprising a cylindrical body portion surrounding said projectile change in diameter in mating surface contact therewith, and a conical portion extending integrally from said cylindrical body portion, said sabot having a longitudinal axial opening therein of uniform diameter surrounding said conically tapered portion of said projectile to form a conically expanding clearance therearound open at one end thereof for accumulating air therein in order to initiate disintegration of said conical portion of said sabot prior to said cylindrical body portion thereof.

2. The combination defined in claim l wherein said open end of said axial opening includes an enlarged entry portion to facilitate the accumulation of air therein.

3. In combination with a gun barrel having a longitudinal bore therethrough for the passage of the expanding gases generated upon the firing of a cartridge therein, a sabot and projectile configuration comprising an elongated subcaliber projectile having an annular decrease in diameter and a conically tapered portion extending therefrom to terminate in a point, a plurality of radially disposed stabilizing fins at the rear end of said projectile, and a sabot of thermosetting plastic material comprising a cylindrical body portion intimately surrounding said projectile in simultaneous gas sealing contact with said annular decrease in diameter and said barrel bore, and a conical portion extending .integrally from said cylindrical body portion to terminate in vertical alignment with said point on said projectile, said sabot having an axial bore therein surrounding said conically tapered portion of said projectile to form a conically expanding annular clearance, said axial bore being open at one end thereof for accumulating air therein during passage thereof through said barrel bore to initiate disintegration of said sabot prior to emergence thereof from said barrel bore.

4. The combination defined in claim 3 wherein said barrel bore includes means forming a plurality of alternately increasing and decreasing diameter portions linearly spaced within the forward two-thirds of the length thereof whereby said cylindrical body portion of said sabot is successively expanded and contracted during passage therethrough to precondition said thermosetting plastic material thereof for rapid disintegration upon emergence from said barrel bore.

5. In combination, a gun barrel having a longitudinal bore therethrough for the passage of the expanding gases generated upon the firing of a cartridge therein, said bore having an enlarged muzzle end portion and a plurality of alternately increasing and decreasing diameter portions linearly spaced rearwardly of said muzzle end portion within the forward two-thirds of bore length, an elongated subcaliber projectile having means forming an annular decrease in diameter and a conically tapered portion extending forwardly therefrom to terminate in a point, a plurality of radially disposed stabilizing tins at the rear end of said projectile of lesser diametrical extent than any portion of said barrel bore, and a sabot of liber-filled thermosetting plastic material having a cylindrical body portion intimately surrounding said projectile in simultaneous gas sealing contact with said annular decrease in diameter and with said barrel bore and having a conically reduced portion extending integrally from said cylindrical body portion to terminate in a frustrum in vertical alignment with said pointed end of said projectile, said sabot having an axial bore therein open at the forward end thereof to form a conically expanding annular clearance surrounding said conically tapered portion of said projectile for accumulating air under pressure during passage thereof through said barrel bore to initiate disintegration of said sabot prior to emergence from said barrel bore, said cylindrical body portion of said sabot being successively expanded and contracted during p assage through said alternately increasing and decreasing diameter portions to precondition said thermosetting plastic material for rapid disintegration upon emergence from said barrel bore.

6. The combination defined in claim 5 wherein said en- 9 larged muzzle end portion of said barrel bore is provided with a plurality of circumferentially spaced parallel knifeedged Wedges for cutting said cylindrical body portion of said sabot during passage therethrough to facilitate the disintegration of said thermosetting plastic material.

7. The combination defined in claim 5 wherein the forward end of said enlarged muzzle end portion of said barrel bore is provided with a plurality of circumferentially spaced parallel knife-edged Wedges of triangular configuration for producing cuts of progressively increasing Width in said cylindrical body portion of said sabot to facilitate the disintegration of said thermosetting plastic material therein, each of said wedges being of progressively increased height to further compress said sabot during the cutting thereof for increasing the preconditioning Of 15 3,033,116

the thermosetting plastic material required for rapid disintegration thereof upon emergence from said barrel bore.

References Cited in the tile of this patent UNITED STATES PATENTS 384,574 Hawley June 12, 1888 2,776,621 Rosenblatt Jan. 8, 1957 2,811,901 Barr Nov. 5, 1957 2,939,395 Barr June 7, 1960 2,983,224 Prosen et al. May 9, 1961 2,983,225 Walker May 9, 1961 2,992,612 Critcheld et al July 18, 1961 2,996,011 Dunlap Aug. 15, 1961 2,996,992 Crtcheld et al Aug. 22, 1961 Critcher et al May 8, 1962 

3. IN COMBINATION WITH A GUN BARREL HAVING A LONGITUDINAL BORE THERETHROUGH FOR THE PASSAGE OF THE EXPANDING GASES GENERATED UPON THE FIRING OF A CARTRIDGE THEREIN, A SABOT AND PROJECTILE CONFIGURATION COMPRISING AN ELONGATED SUBCALIBER PROJECTILE HAVING AN ANNULAR DECREASE IN DIAMETER AND A CONICALLY TAPERED PORTION EXTENDING THEREFROM TO TERMINATE IN A POINT, A PLURALITY OF RADIALLY DISPOSED STABILIZING FINS AT THE REAR END OF SAID PROJECTILE, AND A SABOT OF THERMOSETTING PLASTIC MATERIAL COMPRISING A CYLINDRICAL BODY PORTION INTIMATELY SURROUNDING SAID PROJECTILE IN SIMULTANEOUS GAS SEALING CONTACT WITH SAID ANNULAR DECREASE IN DIAMETER AND SAID BARREL BORE, AND A CONCIAL PORTION EXTENDING INTEGRALLY FROM SAID CYLINDRICAL BODY PORTION TO TERMINATE IN VERTICAL ALIGNMENT WITH SAID POINT ON SAID PROJECTILE, SAID SABOT HAVING AN AXIAL BORE THEREIN SURROUNDING SAID CONCIALLY TAPERED PORTION OF SAID PROJECTILE TO FORM A CONCIALLY EXPANDING ANNULAR CLEARANCE, SAID AXIAL BORE BEING OPEN AT ONE END THEREOF FOR ACCUMULATING AIR THEREIN DURING PASSAGE THEREOF THROUGH SAID BARREL BORE TO INITIATE DISINTEGRATION OF SAID SABOT PRIOR TO EMERGENCE THEREOF FROM SAID BARREL BORE. 